Semiconductor nanocrystals, which are widely known as quantum dots, have a very small size in the range of several nanometers. Thus, the semiconductor nanocrystals exhibit different optical and physical properties from those inherent to bulk semiconductors due to the quantum confinement effect.
As the energy bandgap varies according to a change in size of the semiconductor nanocrystals due to the quantum confinement effect, the semiconductor nanocrystals may exhibit different optical and physical properties depending on the size thereof.
Due to such properties, research and development for applying the semiconductor nanocrystals to various optical elements are actively under way.
In order to apply the semiconductor nanocrystals to optical elements in various fields, semiconductor nanocrystals are generally used by flaking them into polymer resins.
In this case, as a matrix used for flaking of semiconductor nanocrystals, acryl-based or siloxane-based polymer resins having high transparency are widely used.
The siloxane-based resins whose main chain is composed of a siloxane bond have relatively high stability to ultraviolet rays and heat as compared with a hydrocarbon-based polymer resin whose main chain is composed of a carbon bond.
However, when the semiconductor nanocrystals are flaked in a polymer resin, the high surface energy of the semiconductor nanocrystals and incompatibility between organic hydrocarbon based ligand of semiconductor nanocrystals and polymer matrix cause the aggregation of semiconductor nanocrystals.
Accordingly, a process for ligand exchange of the semiconductor nanocrystals which imparts the compatibility with the polymer resin is essentially needed, and also, artificially flaked semiconductor nanocrystals polymer resins are weak in long-term storage stability.
In addition, in order to practically apply the semiconductor nanocrystals to optical devices, reliability that maintains optical characteristics (quantum efficiency) of the semiconductor nanocrystals without deterioration must be ensured, but the semiconductor nanocrystals composed of metals are easily oxidized in an oxidizing environment of heat, oxygen, and moisture, which causes serious deterioration in the quantum efficiency of the semiconductor nanocrystals.
Accordingly, studies and techniques have been previously proposed to solve the problems associated with flaking of the semiconductor nanocrystals in the polymer resin and the problem of being vulnerable to the oxidizing environment.
For example, in order to disperse a semiconductor nanocrystal in a siloxane-based polymer resin, methods for exchanging a conventional organic ligand present on the semiconductor nanocrystal surface with a siloxane-based ligand and the like have been proposed (see International Patent Application Nos. PCT/US2010/001283, PCT/US2013/045244, PCT/IB2013/059577, and PCT/US2011/000724).
However, the methods for exchanging the organic ligand of the semiconductor nanocrystal proposed above have the following problems.
That is, in general, the process of exchanging the organic ligand on the semiconductor nanocrystal surface involves a process by which an existing ligand is desorbed and a new ligand is adsorbed. In this case, defects inevitably occur on the surface of the semiconductor nanocrystals, and this is accompanied by a serious reduction in quantum efficiency, which is an inherent optical characteristic of the semiconductor nanocrystals.
(See Journal of the American Chemical Society, 2003, 125.48: 14652-14653, Journal of the American Chemical Society, 2004, 126.25: 7784-7785, Journal of the American Chemical Society, 2007, 129.3: 482-483, Langmuir, 2008, 24.10: 5270-5276.)
Therefore, there is a need to develop a method for preparing a novel semiconductor nanocrystal siloxane composite resin composition and a cured product which can uniformly flake the semiconductor nanocrystals in the siloxane-based polymer resin without aggregation (that is, achieve uniform dispersion), even without performing an organic ligand exchange process of the semiconductor nanocrystals, and which can effectively protect semiconductor nanocrystals from an external environment to improve reliability of an application element.